When Neil Sedaka kicked off the summer concert series in his native Brighton Beach earlier this month, little did he know that in the audience sat a man who remembered him as a teenage band player at the Shady Nook Hotel in 1960s Catskills, where one was a vacationer and the other an aspiring pop star.

“He was a nice kid, he used to borrow my baseball mitt!” laughed Lou Powsner, a retired Coney Island merchant and Courier Life columnist, who turned 90 years young this month, and who has generated plenty of star power of his own over the last five decades as one of Brooklyn’s most fearless grassroots gladiators, once telling Mayor Bloomberg’s mother why he wouldn’t vote for her “emperor” son. All of his work, he says, has been “to fight the web of crime” that peaked in colicky Coney Island during the Swinging Sixties.

At an age when most people are looking back on their life, Mr. Powsner is looking ahead, with renewed excitement and strong opinions about the future of the borough he has helped shape and steer as a distinguished member of such pivotal Brooklyn organizations as Community Board 13, Kings Highway Board of Trade, Progressive Democratic Club, Bensonhurst West End Community Council, Joint Council of Kings County Boards of Trade, and Coney Island Board of Trade — the last two of which he was also president.

The nonagenarian, a stately World War II veteran with twinkling eyes, strong opinions and an unrelenting constitution, celebrated his milestone birthday on July 14 with two parties, one at the Jewish Association for Services for the Aged’s Scheuer House of Manhattan Beach on Corbin Place, and a “surprise” version at the Mirage Diner on Kings Highway, off East Seventh Street, both of which he drove his own car to. Nor does he show any signs of slowing down just because the calendar says so. He even conducted this phone interview while grocery shopping. Then again, Mr. Powsner, whose family relocated to Brooklyn from Crandon (pop. 72), South Dakota, when he was two years old, has a habit of defying the odds.

Born in 1920, when the first radio show aired, women voted for the first time and Warren Harding was elected president, he has seen his share of hard times, and lived to tell the tale. But only just, after being held up “seven or eight times” and seeing two of his fellow retail colleagues killed in brutal, cold-blooded hold-ups, one of them discovered sitting on the toilet with his throat slit. In his quest “for survival,” Mr. Powsner assisted cops in 79 arrests during the 44 years he ran a men’s apparel and furnishings shop on Mermaid Avenue, one block north of Steeplechase Park, which his father opened in 1923.

One cold winter day in 1979, he recalled relaxing with a newspaper when three teenagers walked in and asked to view his Cortefiel collection of fine leather goods. As he went to the coat rack, he said he noticed another teen enter, who shouted, “Get your motherf—–’ ass down on the floor.” The thugs bound his hands, feet and mouth with his own neckties, peeled the Spanish leather coats off the rack and emptied the contents of the register into a brown paper bag, containing his uneaten lunch — a recollection which still makes Mr. Powsner chuckle — before fleeing on foot.

Crawling “like a snake across the floor” to his alarm system, he managed to alert cops and, within minutes, was helping them hunt down the suspects in a patrol car, nabbing one in the nearby Mermaid Houses on Neptune Avenue, between West 33rd and West 35th streets, and two more within the hour. The next day, at the preliminary hearing in Brooklyn Criminal Court, the robber’s mother rushed up to him, says Mr. Powsner, who helped the woman get an apartment in the O’Dwyer Gardens city housing complex on Mermaid Avenue and West 21st Street when it first opened on New Year’s Eve 1969. “She said, ‘I don’t know how to apologize to you after what you did for us,’” remembered the man. “I said to her, ‘I should be the one apologizing to you because I helped bring you into what turned out to be a penitentiary for the poor’.”

One of the three thugs escaped and wasn’t caught until 14 years later when he was apprehended in connection with another felony, an event which splashed Mr. Powsner across city headlines — once more. The fourth suspect remained on the lam until 2003 when he was arrested for an unrelated offense, and convicted of the crime he had committed in Coney Island 24 years earlier.

Those who know him say the mold was broken when Mr. Powsner was created.

“He’s a unique individual, the most tenacious one I’ve ever met, and comparable to a high-tech computer,” quipped Bensonhurst West End Community Council President — and fellow Courier Life columnist — Carmine Santa Maria, whose column, “Big Screecher” has run alongside Mr. Powsner’s “Speak Out” for the past 32 years. Added Santa Maria, whose page mate is his group’s first vice president, “He’ll fight you toe-to-toe to prove that he’s right — and he usually is.”

The Teflon titan thinks nothing of taking on tough opponents, either. In a recent column, “Bloomberg’s blunders strike again,” he opines, “For eight years, Mayor Bloomberg would call a Coney Boardwalk press conference to pledge to bring back the old Coney Island, then he would trip over protruding nails walking to his car.”

Mr. Powsner also has a few choice words for Coney Island’s ongoing renaissance. His views on Borough President Markowitz’s amphitheater project? “It’s the right thing in the wrong place; there should not be a roof over a park.”

He prefers a wooden boardwalk, too. “I have seen what can happen to a cement boardwalk. The Manhattan Beach Esplanade has been fenced off since the ’60s, after Hurricanes Bonnie and Donna made it vertical.”

Then, there’s his prescription for a better Coney: “a couple of hotels. They would be a primer to developing because with them come shops and restaurants. The rides sound nice, but they’re prisoners of the skies; when it rains, it’s like a cemetery.”

A widower, father of two, grandfather of five, and great-grandfather of one, Mr. Powsner lives alone “with God” in the Bensonhurst home he shared with his late wife, Irene, where the couple raised daughter Bonnie, who watches over him “like a hawk,” and son Farrel, a retired math chairman of John Dewey High School.

He enjoys an active social life with his companion, Ruby, attends more than a dozen Broadway and off-Broadway shows a year — his most recent was “My Big Gay Italian Wedding” — and is a regular face at the civic meetings where he continues to champion a better quality of life for his fellow boroughites.

In fact, next time you pass a cop on a walkie-talkie, think of Mr. Powsner, who turned the city onto them in the late ’60s with help from late pal and fellow Joint Council member Al Sinrod, a former medic, who used the devices to communicate with his infantry unit in World War II: “Before then, the city had police boxes that the cops would use to call in for help, but sometimes, those phones would be stolen!”

And, think of Mr. Powsner when you pass a city street lamp. His brilliant idea to combat crime in the mid-1960s — “illuminate the streets better” — caught on across the Big Apple as officials wised up to the benefits of Lucalox lighting, still used today. Credit for that is due, in large part, to the venerable activist, who began a years-long crusade — taking him to the highest levels of government — when he invited a Con Edison representative to a humble meeting of the Joint Council for a slide show presentation on the high pressure sodium light bulbs which, at the time, were only used in Pueblo, Colo., and Kansas City, Kan.

“I typed out a petition, ‘Do you prefer crime or bright lights?’” said the everlasting activist, who dispatched a young district leader named Howard Golden — Brooklyn’s future borough president — to pound the pavement.

“You fight for what’s right,” he said. “If you put your muscle behind it, you can accomplish great things.” Some of those “great things” are yet to come our way, thanks to the great likes of self-declared “honorary Brooklynite” Lou Powsner.